Demand for electric power during daytime on a weekday is very large compared to demand for electric power during nighttime. Therefore, in the past, a nuclear power station and a steam power station using a steam turbine are always operated regardless of daytime and nighttime, and a hydraulic power station and a thermal power station using a gas turbine (for example, a combined cycle power station) are operated only during daytime. Further, electric demand and electric supply are balanced by pumping up water to a reservoir to a high level by driving a pump using surplus power during nighttime (power left over at the nuclear power station and the steam power station) to store as potential energy, and allowing the water to flow down during daytime, as in a pump-up hydraulic power station. In recent years, a ratio of the maximum electric demand to the minimum electric demand is gradually being increased due to wide use of home air-conditioners, and difference in seasonal dependence of the electric demand is particularly increased. Since the period necessary for the maximum electric demand is as short as around ten days in the summer, it is uneconomical to install a large scale electric generating facility for coping with solely this problem. On the other hand, there remain few sites capable of constructing a scale pump-up hydraulic power station in certain areas, and accordingly a large capacity energy storage method of another type is required to be developed.
In regard to energy storage gas-turbine electric power generating systems capable of storing energy having a gas turbine and air liquefaction/storage/vaporizing facilities, Japanese Patent Application Laid-Open No.4-132837 discloses a system in which recovery heat from the liquefaction facility and exhausted heat from the gas turbine plant are used inside and outside the electric power facility as a heat source. Further, Japanese Patent Application Laid-Open No.4-191419 discloses a system in which liquid air or liquid oxygen is produced and stored using electric power in nighttime, and vaporized in daytime to be supplied to the gas turbine.
However, in the system of Japanese Patent Application Laid-Open No.4-132837, the energy storage efficiency (a ratio of an electric power for obtaining the liquid fluid such as liquid air or liquid oxygen to an electric power generated by the plant) is not so high. In the system of Japanese Patent Application Laid-Open No.4-191419, there is no detailed description of improving the energy storage efficiency.